Mobilization of internal Ca2+ by vasoactive intestinal polypeptide in endothelial cells.
The aims of the present study were to establish whether vasoactive intestinal polypeptide (VIP) could mobilize internally-stored Ca2+ and whether Ca2+ release could trigger Ca2+ influx from the extracellular space. Bovine pulmonary artery endothelial cells from an established cell line were loaded with fura-2/AM and cells were studied in suspension or were imaged in monolayers at 40-80% confluency. In Ca2+ imaging studies, VIP evoked Ca2+ transients in Ca2+-free medium containing 50 microM EGTA. This was observed in 33 out of 122 cells examined on 29 separate trials. With each cell, the spread of Ca2+ appeared to occur from the periphery of the cell to the central core. Cells which did not respond to VIP responded to other stimulants such as bradykinin, endoplasmic reticulum Ca2+ pump inhibitors, (cyclopiazonic acid and thapsigargin), and endoplasmic reticulum Ca2+ release channel opener, ryanodine. The reintroduction of Ca2+ following VIP-induced Ca2+ release did not evoke a Ca2+ response in 5 cells imaged. Cells in suspension showed typical biphasic responses to bradykinin, thapsigargin or cyclopiazonic acid in the presence of external Ca2+. Stimulation with VIP caused transient Ca2+ responses in Ca2+-free physiological saline containing 50 microM EGTA. However, only 1 out of 4 cells tested showed a response to Ca2+ when it was reintroduced to the bathing medium. This study provided direct evidence for the first time in these bovine endothelial cells for VIP-mediated elevation of cytosolic concentration of Ca2+. The results also suggested that other mechanisms might prevail preventing capacitative Ca2+ entry following the release of internally-stored Ca2+.
Low
A M
AM
Department of Biomedical Sciences, McMaster University, Hamilton, Ont., Canada.
Sormaz
L
L
Kwan
C Y
CY
Daniel
E E
EE
D000818:Animals; D001920:Bradykinin / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D018929:Cell Culture Techniques; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D011651:Pulmonary Artery / Q000187:drug effects*; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism / Q000494:pharmacology*
D005456:Fluorescent Dyes; D014660:Vasoactive Intestinal Peptide; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2